In high energy repetitively pulsed gas lasers, efficiency, repetition rate and beam quality are important considerations but are elusive in practice. Conventional repetitively pulsed gas lasers employ a pump or the like for directing a continuous flow of gas through the lasing cavity. See, for example, U.S. Pat. Nos. 3,886,481; 4,000,477; 4,005,374; 4,031,484 and 4,118,592. Since it it desirable to have the gas quiescent and uniform in the lasing cavity at the time of discharge, acoustic suppressor and absorber elements are often employed, with consequent increase in resistance to gas flow. Additionally, interaction of gas pressure waves with acoustic and flow-directing elements may produce inhomogeneities in the lasing medium, which would necessitate low repetition rate to obtain reasonable beam quality. Moreover, substantial energy is required for operation of pumping, heat exchange and/or reconditioning of the gas, which leads to reduced overall efficiency.
Gubarev et al, "Possibility of Spontaneous Circulation of a Gas Mixture in a Pulse-Periodic Laser," Sov. J. Quan. Elec., July 1978, suggests that pressure waves resulting from residual thermal energy in the laser cavity may be employed for stimulating gas circulation by disposition of a gas valve upstream of the laser cavity and an acoustic resonator downstream of the lasing cavity. The gas valve is to be manipulated as a function of shock wave travel within the resonator for drawing fresh gas through the valve into the discharge cavity.
An object of the present invention is to provide a method and apparatus for circulating the lasing medium in a repetitively pulsed gas laser which minimizes or overcomes the above-noted difficulties in the prior art. A more specific object of the invention is to provide improved method and apparatus of the described type which manipulate the pressure waves generated by residual thermal energy in the cavity gas for effecting gas circulation, while maintaining the lasing gas in the cavity substantially quiescent and uniform during the lasing event.